Investigation of Rh/Nr3 Catalytic Systems in Sequential Stages of Reductive Hydroformylation Engaging in Situ X-Ray Absorption Spectroscopy

Abstract

Nowadays reductive hydroformylation over Rh/NR3 catalysts is of great interest to both industry and academia, however, some of its aspects remain controversial or unclear, including those which might turn essential for developing new active catalysts and optimization of parameters. In this work, we studied in depth separately both stages of the process – hydroformylation of olefins and hydrogenation of aldehydes, – and estimated the role of the amine structure in them. Also, for the first time, we investigated Rh/NR3 catalytic system under the reaction conditions by in situ XAS method to gain the additional structural information, and observed the correlation of the obtained data with the results of catalytic experiments. Catalytic and in situ XAS measurements shown that tertiary amines suppress Rh clusterization, forming species of lower nuclearity. These Rh/amine species may include both charged and uncharged ones. The addition of amines, which are effective promotors of the hydrogenation step, decelerates hydroformylation, presumably, through the formation of amine containing Rh complexes.

Keywords: Reductive hydroformylation, rhodium complexes, x-ray absorption spectroscopy, XANES, EXAFS, in situ measurements, amines